Ventricular fibrillation occurs as a side effect of contrast media in coronary arteriography about 1 percent of the time. The long term objectives of this work are to define the chemical, physiologic, and pathologic factors which contribute to or enhance the incidence rate of fibrillation. In vitro experiments will be performed to describe calcium binding by contrast media and the influence of hypertonic contrast media on cell volume. Organ perfusion experiments will be performed to monitor tissue fluid and electrolytic shifts produced by selective arteriography. More direct examination of factors influencing fibrillation will be studied in experiments on anesthetized dogs. Contrast media will be injected into the right coronary artery until fibrillation occurs. The influence of calcium binding agents, cardiac glycosides, catecholamines, acute and sub-acute myocardial infarction, and other factors on fibrillation dose will be determined. Coronary arteriography is a valuable and widely used clinical procedure. A better understanding of the factors influencing the incidence of fibrillation will allow better identification of patients who have a higher risk and will allow the development of even safer contrast material.